1. Field of the Invention
This invention relates in general to the field of microelectronics, and more particularly to an apparatus and method for reducing interference in a wireless communication system.
2. Description of the Related Art
The cell phone industry is undergoing exponential growth, not only in the this country, but all over the world. In fact, it is well known that the over twenty percent of the adult population in the United States do not even have a traditional landline telephone. In addition to those who do not own a conventional telephone, nearly ninety percent of the adult population owns a wireless phone.
And the usage of cell phones is increasing as well over the use of traditional landline telephone coverage. In fact, one in seven adults now uses only cell phones. Whereas in the past cell phones were used when a landline was not available or under emergency conditions, lower carrier rates, affordability of family packages, and free mobile-to-mobile or friend-to-friend promotions have fostered in significant increases in usage. It is not uncommon today to walk into any public forum or facility and notice a majority of the people there talking on their cell phones.
The ability to communicate using a mobile phone, or mobile station, has been available since the middle of the last century. However, during the 1990's so-called “2G” or second generation mobile phone systems were provided that began the growth in both deployment and usage that we currently enjoy today. These initial systems prevalently employed frequency division multiple access (FDMA) as the modulation strategy. One well known example of this technology is Global System for Mobile Communications (GSM), in which a particular cell phone communicates with its base station within a given cell over a specific frequency channel. In order for that cell phone to communicate with a base station in an adjacent cell, it must be assigned a new frequency channel and the switch coordinated in time with the old base station, the new base station, and the cell phone itself. This type of handoff from one cell to the next is known as a hard handoff.
Currently, so-called “3G” or third generation cellular communications technologies are being developed. These technologies are not characterized so much by modulation techniques, but more so by performance metrics (e.g., 2 Megabits per second indoor data rates, 384 Kilobits per second outdoor data rates). As such, there are presently a number of diverse approaches being proposed for 3G.
In the interim, a number of hybrid technologies are being provided, known as “2.5G” techniques and protocols, one of which is CDMA2000, which is also known as IS-95. This system utilizes spread spectrum code division multiple access (CDMA) techniques to multiplex many users over a single frequency channel thus providing capacity improvements over that which can be attained through the use of current FDMA systems. Under CDMA, the same frequency channel is used to communicate with all of the mobile stations within a group of adjacent cells and signals to and from the mobile stations are uniquely encoded using orthogonal codes.
Since the same frequency channel is used to communicate with multiple cell phones, the preclusion and reduction of interference is highly desirable, and numerous techniques and methods are extant within the art to enable adjacent mobile stations to communicate with their base station controllers without causing undue interference. One such technique is called closed loop power control.
Under this technique, information is regularly and frequently exchanged between a base station and a mobile station about the power level that is being received and requests are made to either increase or decrease that power level in order to maximize signal to noise ratio for those signals relative to other signals that are being received. In a present day scenario, these messages are exchanged roughly every five milliseconds.
But there are also several other techniques that is employed in a present day CDMA-based wireless communication system to reduce interference such as smart blanking and early message termination, which do not entirely comport with the protocol that is defined by IS-95 for the exchange of power control information. For example, there is only one timeline that is defined by IS-95 for the exchange of power control information between a mobile station and a base station, and often times it has been observed that this timeline is restrictive in the presence of smart blanking. That is, when smart blanking is enabled, the latency for implementing power control measures essentially doubles. What this means is that it takes longer for, say, a base station to request a transmit power level adjustment in a corresponding mobile station. And vice versa.
The present inventors have also observed under other circumstances, say early termination where a mobile station has acknowledged reception of a message in mid-frame and the base station has terminated transmission of traffic early, the protocol dictates that power control information still be sent as the same frequency for the remainder of the frame.
Therefore, what is needed is an apparatus and method whereby power control timelines between a base station and a mobile station can be adaptively modified to provide for reduction in the latencies associated with affective power control.
In addition, what is needed is a mechanism in both mobile stations and base stations that enables an optimum power control timeline to be selected from among several timelines in order to reduce latencies or to optimize other system parameters.
Furthermore, what is needed is a technique for increasing and decreasing the transmission of power control information between a base station and a mobile station under so-called smart blanking scenarios.
Moreover, what is needed is a method for dynamically reducing the rate of power control information by a base station when the base station stops transmitting traffic due to early acknowledgement by a receiving mobile station.